The present invention relates to a method and an apparatus for laser welding together two or more sheet blanks along a seamline, and more particularly, to an apparatus which adjusts the focal intensity of the laser beam energy on the seamline and/or weld time to compensate for variations in the spacing between the edges of the blanks to be joined.
Present day manufacturing requirements often necessitate the formation of various workpiece components by welding together two or more sheet metal blanks. More frequently, lasers have been used to weld abutting edge portions of the sheet blanks along seamlines in the formation of workpiece components.
Conventional laser welding apparatus have suffered the disadvantage in that heretofore, the use of lasers to weld the blanks together has necessitated that the edges of the sheet blanks be pre-finished and have a mirror-smooth finish. The requirements of blank edge preparations have to a large extent been responsible for the reluctance by industries to adapt the use of laser welding apparatus in continuous scam welding processes used to form sheet blanks.
Conventional laser apparatus have suffered the further disadvantage in that to ensure the formation of a complete weld and prevent butt-weld seams having concavity, it is necessary to ensure precise abutting contact between the proximal edges of the sheet metal blanks along the entire length of the weld seam. The necessity of maintaining the sheet blanks in precise contact during welding disadvantageously results in an increase in workpiece production time as a result of the necessity of ensuring the blanks are in an exact abutting position prior to welding.
The inventor has appreciated an improved apparatus for butt welding together sheet metal blanks which incorporates a yttrium aluminum garnet (YAG) laser, and has disclosed the operation of such an apparatus in pending Canadian patent application Serial No. 2,167,111, which was filed Jan. 15, 1996. The use of a YAG laser to butt weld together sheet blanks advantageously has been found to produce weld seams without a concave weld profile, where gaps of up to 0.1 mm exist between the sheet blanks.
The applicant has, however, appreciated that providing an apparatus which may effectively butt weld sheet blanks which are separated by larger gaps, would facilitate workpiece production by requiring less stringent positioning and edge finishing of the sheet blanks prior to welding. This, in turn, would increase production time and reduce sheet blank manufacturing cost.
To at least partially overcome the disadvantages of the prior art, the present invention provides a welding apparatus for use in industrial processing, which is operable to emit an energy beam or ion beam (hereinafter collectively referred to as an energy beam), to weld blanks and the like together along a seam line. The energy beam used to weld the blanks preferably consists of a multiple beam of two or more coherent light sources. The apparatus includes a mechanism to selectively reposition the orientation of the multiple beam relative to the seamline.
Another object of the invention is to provide an apparatus for butt welding together proximal edge portions of two or more sheet blanks which are separated by a gap of up to 0.25 mm or more.
Another object of the invention is to provide an apparatus for laser welding together two or more sheet blanks, without requiring the edge portions of the blanks to be pre-finished.
A further object of the invention is to provide an apparatus for joining together workpiece blanks to form a composite workpiece, and which does not require precise alignment and positioning of the blanks prior to joining.
Another object of the invention is to provide an apparatus for welding together proximal edge portions of sheet blanks having different relative thicknesses.
A further object of the invention is to provide an apparatus for laser butt welding together two or more sheet blanks along a seamline, and which automatically senses the spacing between proximal edge portions of the sheet blanks and compensates either the speed and/or positioning and/or power of the laser energy to ensure the formation of an effective weld seam across the proximal portions.
Another object of the invention is to provide a laser welding apparatus adapted to weld proximal edge portions of sheet metal blanks along either straight, non-linear or curved weld seams.
To achieve at least some of the foregoing objects, the present invention includes a welding apparatus for welding together proximal edge portions of two or more sheet blanks. The welding apparatus is configured to emit a multiple or composite energy beam which consists of two, three or more energy beams. Preferably, the energy beams are laser beams or coherent light sources used to weld the sheet blanks together along a seamline, however, the use of the invention with other energy beams such as ion or electron beams and the like is also possible and will operate in a like manner.
The coherent light sources or laser beams which make up the composite beam are focused towards a portion of the blanks to be welded together at respective focal area or focal spot. The focal areas of each of the laser beams have an optic centre, wherein the optic centres of at least two of the laser beams (i.e. a first laser beam and a second laser beam) which make up the composite beam are spaced or offset from each other.
The spaced optic centres of the first and second laser beams provide the composite beam with a beam energy or intensity profile which is elongated in the orientation of the optic centres. The optic centres of the laser beam may thus be said to each define one end of a focal line of elongation of the composite beam.
The composite beam of laser energy is emitted from a laser head which is movable over the workpiece blanks. The apparatus further includes mechanisms to vary the intensity per unit area of the composite beam. For example, the laser head is preferably rotatably mounted to move the focal line of the composite beam relative to the proximal edge portions of the blanks to be welded. The beam may be moved between a position wherein the focal line is positioned substantially normal to the proximal edge portions of the blanks and a position wherein the focal line is oriented in a position substantially aligned with the proximal edge portions of the workpieces which are to be welded.
Other suitable mechanisms to alter the beam intensity per unit area also would include a drive mechanism used to vary the speed at which the laser head moves over the seamline, or a power regulator used to vary the output power of the laser beams.
The coherent light sources making up the composite beam may, for example, comprise almost any type of laser beam, including CO2 lasers. More preferably, however, high energy lasers, such as yttrium aluminum garnet (YAG) lasers are used to weld the blanks.
The laser head is preferably movably provided in the apparatus to move the composite beam relative to the sheet blanks along a predetermined or sensed linear and/or curved path. The laser may thus be activated and the laser head moved along its sensed/predetermined path to weld proximal edges of the sheet blanks together along a seamline.
More preferably, the apparatus includes a sensing mechanism for sensing the spacing between abutting edge portions of the blanks to be welded. A microprocessor control is provided to rotate the laser head or fiber optic connectors relative to the seamline in response to the sensed spacing. In this manner, the composite beam may be selectively rotated to move the focal line. The focal line may be rotated to a preset orientation relative to the portion of the seamline which is to be formed, as for example, in an orientation at or between a position normal to the abutting edge portions of the blanks and a position substantially aligned thereover.
Where a gap exists between the abutting edge portions of the blanks which are to be joined, the composite beam is positioned so that the optic centres of the first and second laser beams are each located on a respective edge portion of each blank, with the focal line of the composite beam straddling the gap. This position provides a maximum spread of laser energy across the gap producing the maximum infill of molten metal into the gap from the edge portions of the blanks.
Where no gap exists between the abutting edge portions of the blanks, the laser head may be rotated so that the composite beam is positioned with its focal line moved towards or into alignment with the seamline. In this position, the laser energy is focused along the seamline which is to be formed. This advantageously concentrates the intensity of the laser energy along the seamline and decreases the time required to form a complete weld seam, enabling a finished blank to be produced with higher weld speeds.
More preferably, the speed of movement of the laser head above the blank is controlled having regard to the degree of spacing between the proximate portions of the blanks and/or the orientation of the focal line of the composite beam relative to the seamline which is to be formed. As indicated, if desired, the power output of the energy beam could also be varied with any sensed spacing between the abutting edge portions of the blanks. In this manner, higher energy outputs may be provided when the focal line of the beam energy straddles any gap and lower beam energy used when the focal line is aligned with the weld seam.
Accordingly, in one aspect, the present invention resides in an apparatus for joining together proximal edge portions of two workpicce blanks along a seamline comprising,
laser means for emitting a composite beam to weld said blanks together along said seamline,
said composite beam including a first laser beam and a second laser beam, each of said first and second laser beams being focused towards a portion of said blanks to be welded at respective focal areas having an optic centre, wherein the optic centres of said first and second laser beams are offset from each other and each define one end of a focal line of said composite beam,
rotation means for selectively rotating said laser means to move said focal line relative to said portion of said blanks between a position wherein said focal line is oriented substantially normal to said portion of said seamline, and a position wherein said focal line is oriented substantially aligned with said portion of said seamline.
In another aspect, the present invention resides in a laser apparatus for welding together abutting edge portions of two sheet blanks along a seamline, the apparatus comprising:
a laser head operable to emit laser energy to weld said blanks together along the seamline,
rotation means for rotating the laser head and change the orientation of said laser energy relative said seamline,
wherein said laser energy comprises a multiple beam of at least two offset laser beams.
In a further aspect, the present invention resides in a method as claimed in claim 15, wherein said apparatus further includes sensing means for sensing spacing between the abutting portions of the blanks, and
wherein said method includes the further step of sensing the spacing between the adjacent portions of the blanks at said portion of said blanks to be welded prior to moving said focal line therealong, and
wherein said preset position of said focal line is determined by the sensed spacing between the adjacent portions of the blanks.
In another aspect, the present invention resides in an apparatus for joining together proximal edge portions of two workpiece blanks along a seamline comprising,
means for emitting a composite energy beam to weld said blanks together along said seamline,
said composite energy beam including a first energy beam and a second energy beam, each of said first and second energy beams being focused towards a portion of said blanks to be welded at respective focal areas having a centre, wherein the centres of said first and second laser beams are offset from each other and each define one end of a focal line of said composite energy beam,
sensor means for sensing any spacing between the proximal edge portions of the blanks, and means for changing the beam intensity per unit area selected from the group consisting of,
rotation means for selectively rotating said means for emitting said composite energy beam to move said focal line relative to said portion of said blanks between a position wherein said focal line is oriented substantially normal to said portion of said seamline, and a position wherein said focal line is oriented substantially aligned with said portion of said seamline,
drive means for moving said means for emitting said composite energy beam along said seamline, said drive means activatable to vary the speed of movement of said laser beam depending on the sensed spacing between the proximal edge portions of the blanks, and
power regulating means to vary the composite energy beam energy output depending on the sensed spacing between the proximal edge portions of the blanks.